Batteries for medical devices have demanding requirements. They should be small, have a long life, high power output, low self-discharge rate, compact size and high reliability. The need for miniaturization while maintaining or increasing output means that as much of the battery footprint as possible should be used for power storage resulting in the concomitant elimination of dead space. However, while the elimination of dead space should result in greater miniaturization, it also results in a greater difficulty of assembly due to the increasingly small size of the component parts.
Traditionally, jelly roll type batteries have been made by using a mandrel to wrap electrodes around. Once wrapped, the mandrel is removed providing a jelly roll wrapped electrode assembly for use in a battery. However, removal of the mandrel from the core of the jelly roll inherently presents the potential of damaging the jelly roll due to the possibility of pulling the core of the jelly roll out with the mandrel. Therefore, the jelly roll should not be wrapped tight to avoid this problem. Conversely, a loosely wrapped jelly roll wastes space and decreases battery capacity and power due to size constraints. More recently, jelly roll storage batteries have been made using a rod-shaped, non-conductive, non-deformable core around which electrodes are wrapped. Conductive tabs are added to each electrode to complete the circuit.
U.S. Pat. No. 7,442,465 to Kim et al., discloses a rechargeable battery which has a non-deformation core. Once the positive and negative electrodes are wound around the core, conductive tabs are attached to the electrodes and the core serves to prevent deformation of the jelly roll, but does not conduct current.
U.S. published patent application U.S. 2003/0134185 to Nakahara et al. describes a feedthrough pin that is directly connected to an inner end of an electrode. The pin extends from the jelly roll and through the battery case and functions as a battery terminal. The feedthrough pin fits into a slotted ‘C’-shaped mandrel. The positive electrode is conductively connected to the pin which fits within the ‘C’-shaped mandrel. As the positive electrode is wound, a separator is inserted between the feedthrough pin/mandrel and the positive electrode. A negative electrode is inserted between the separator and the pin/mandrel. The separator and negative electrode are held in the jelly roll by the tension created between the feedthrough pin/mandrel and the positive electrode. After winding, a metal tab is welded to the negative electrode and the tab contacts the battery case endcap to complete the circuit.
Both of the aforementioned batteries require the placement of at least one tab on an electrode to complete the circuit during or after winding the electrodes. In either case, the passive connection of one of the electrodes to the case is required for the circuit to be completed.
Therefore, a need exists for an improved electrode assembly.